function add() {
    console.log('add')
}
function del() {
    console.log('del')
}
function reduce() {
    console.log('reduce')
}
function select() {
    console.log('select')
}


// 导出方法: (exports / modules.exports.成员名 = 值)
// exports.add = add;
exports.del = del;
exports.reduce = reduce;
exports.select = select;
// module.exports === exports

// 上面写法也能这么写
module.exports.add = add;